EAK is dangerous when stored in large quantities, particularly at elevated temperatures. For example, when EAK is heated to a typical casting temperature of about 100.degree. C., a compact mass of more than about 500 pounds, or 37 gallons, of EAK exceeds its critical mass and will explode. For this reason, EAK can only be safely handled in small quantities, or at a temperature substantially below 100.degree. C.
There are several known processes for manufacturing EAK. One such method is the alcohol process. In this process, nitric acid is added to a solution of ethylene diamine in ethanol or methanol; the product is ethylene diamine dinitrate. The latter material is filtered, washed, dried, melted, and combined with molten potassium nitrate and ammonium nitrate to produce EAK. One disadvantage of this process is that the solvents used in this process are flammable, so they do not substantially reduce the risk of handling ethylene diamine dinitrate (which is also a heat-sensitive explosive). The need to melt EAK is also a problem with this method. Furthermore, this is not a continuous process, due to the need to keep the amount of molten EAK below its critical mass as specified above. The primary advantage of this prior process is that ethylene diamine dinitrate can be removed from solution by filtering.
A second process which has been used to form EAK is the perchloroethylene process, in which ethylene diamine dinitrate is formed in perchloroethylene by the reaction between nitric acid and ethylene diamine. Ammonium nitrate and potassium nitrate are added to the mixture, its temperature is raised to melt EAK, and the mixture is then chilled with cold perchloroethylene to form granules of EAK. Three important disadvantages of the perchloroethylene method are that perchloroethylene participates somewhat in the reaction, perchloroethylene is occluded in the resulting granules, and the boiling point of perchloroethylene is sufficiently higher than 100.degree. C. that any exotherm of EAK or its components will not be regulated by evaporation of the solvent to remove heat from the reaction mixture.
Another known process for forming EAK is the double-direct method. Here, ethylene diamine is added to a solution of ammonium nitrate and potassium nitrate in aqueous nitric acid (70%) at 60.degree. C. The mixture is heated to 110.degree. C. and a vacuum is applied to remove the water and nitric acid from the reaction mixture. Besides the previously described danger of maintaining a substantial quantity of EAK at 110.degree. C., this process is not continuous, and requires a costly and time consuming vacuum stripping and solvent recovery process.
Still another EAK production process is the water process. This process, which has been proposed but apparently not tried, requires that liquid ammonia, then ethylene diamine, then potassium hydroxide be sequentially added to a 60% nitric acid solution. These added constituents form ammonium nitrate, ethylene diamine dinitrate, and potassium nitrate by reacting with nitric acid. The remaining water is then removed by a triple-effect evaporator and a wiped-film evaporator to produce dry EAK. It has been proposed to practice this as a continuous process. Again, however, the residual water must be removed by drying, which requires energy and time.
To summarize, prior processes mostly have been batch processes, have required that solvents be removed by evaporation, and have in some cases required heating of concentrated ethylene diamine dinitrate or EAK.